Next generation wireless networks are likely to rely on higher frequency, lower wavelength radio waves, including for example the use of mm-wave technologies within the 24-100 GHz frequency band. At these frequencies, larger aperture and more directive antennas are likely to be used to compensate for higher propagation losses. Common technologies for large-aperture mm-wave antennas are lens and reflector antennas.
There has been growing interest in developing beam scanning antennas that rely on exploiting the anisotropy properties of liquid crystal to form a beam steerable reflector or reflectarray. Much of the interest has focused in either structures that employ a variable delay line using liquid crystal to achieve beam steerable phased array, or structures that operate in reflective mode using a large liquid crystal loaded reflectarray. Some attempts also have been made to use liquid crystal to form a tunable reflection polarizer. Although liquid crystal is potentially useful for many reconfigurable microwave devices, use of liquid crystal as a direct delay line tends to suffer from significant losses. As a result, operating liquid crystal as a direct delay line can only be limited to a small phased array. Forming a tunable reflective surface or reflectarray using liquid crystal has a disadvantage of a large F/D (Focal Distance/Aperture Size), which results in an antenna with an undesirably large profile. Furthermore, a tunable reflective surface also suffers relatively high loss at resonant frequency which results in low aperture efficiency.
Low profile, millimeter wave planar antennas which are capable of multi-beam transmission for multiuser MIMO (multiple-input, multiple-output) schemes and high-gain point-to-point transmission are needed for future 5G deployment. Accordingly, there is a need for a re-configurable, space-efficient lens antenna structures suitable for small wavelength applications.